Steel Wire Having Excellent Straightness Quality and Manufacturing Method Thereof

ABSTRACT

Provided are a steel wire having excellent straightness quality and a method of manufacturing the steel wire, wherein the steel wire includes a wire, after undergoing a drawing operation, undergoing a heating operation of performing heating in a state in which tension is applied, and undergoing a cooling operation, wherein, when winding the wire around a winding portion having a diameter greater than a diameter of the wire for a preset period of time and then measuring straightness of the wire of 400 mm, the straightness of the wire is less than or equal to 30 mm, and the method includes a wire preparation operation, a heating operation, a cooling operation, and a straightness measurement operation.

TECHNICAL FIELD

The present disclosure relates to a steel wire having excellent straightness quality and a manufacturing method thereof, and more particularly, to a steel wire having excellent straightness quality and a manufacturing method thereof, wherein as the steel wire is heated at a preset temperature or higher for a short period of time, strain aging of the steel wire may be promoted to improve straightness quality after aging.

BACKGROUND ART

In general, steel wires have been used in various industrial fields and have been used for vehicle tires, industrial belts, and the like. Steel wires used for various purposes as described above are needed to have various quality characteristics. In particular, when steel wires are used as tire reinforcement materials, the straightness of the steel wires is needed.

Steel wires used in the industrial fields are not used immediately after the steel wires are manufactured but are used several months after the steel wires are wound and stored around spools having preset inner diameters. However, when the steel wires are used after being wound and stored around the spools as described above, the straightness of the steel wires is not maintained.

When the straightness of the steel wires is not maintained, the steel wires may not be used in the industrial fields needing the straightness. In detail, if straightness is poor when steel wires are used as tire reinforcement materials, the poor straightness may affect work processability when manufacturing tires and may cause buckling and tip rising phenomena, and thus, tire manufacturers may have difficulty in rolling and cutting processes. Also, when the straightness of steel wires is not maintained, the steel wires may be difficult to be used in various fields needing the straightness of the steel wires.

The straightness of steel wires changes because of the following causes. Steel wires use carbon steel as a material thereof, and interstitial solid solution atoms C and N exist in the carbon steel and diffuse over time to move to and fix to adjacent potentials. Therefore, when steel wires are manufactured and wound around spools having preset inner diameters, the straightness thereof changes due to the diffusion and fixation of atoms C and N and thus deteriorates.

Existing steel wires may not provide steel wires having excellent straightness due to drawbacks as described above. In other words, although existing steel wires have excellent straightness characteristics at the beginning of manufacturing, after the existing steel wires are wound around spools having preset inner diameters and a long period of time passes, the straightness characteristics thereof change due to strain aging under stress within an elastic section and thus do not satisfy straightness quality characteristics.

DESCRIPTION OF EMBODIMENTS Technical Problem

Provided are a steel wire having excellent straightness quality and a manufacturing method thereof, wherein as the steel wire is heated at a preset temperature or higher for a short period of time, strain aging of the steel wire is promoted to improve straightness quality after aging.

Solution to Problem

According to an aspect of the preset disclosure, a steel wire having excellent straightness quality, may include a wire, after undergoing a drawing operation, undergoing a heating operation of performing heating in a state in which tension is applied, and undergoing a cooling operation, wherein, when winding the wire around a winding portion having a diameter greater than a diameter of the wire for a preset period of time and then measuring straightness of the wire of 400 mm, the straightness of the wire is less than or equal to 30 mm.

A heating temperature in the heating operation may be about 80° C. to 220° C.

The heating temperature and a heating time in the heating operation of the wire may satisfy Equation A below, and the heating temperature in the heating operation may be higher than or equal to 80° C., wherein Equation A: T+15.67 ln(t)≥300, wherein T denotes absolute temperature K of the heating temperature, and t denotes the heating time s.

The heating time in the heating operation may be about 0.02 s to about 10 s, and tension applied to the wire in the heating operation may be about 1% to about 50% of a cutting strength.

According to another aspect of the present disclosure, a method of manufacturing a steel wire having excellent straightness quality, may include: a wire preparation operation of preparing a wire that is drawn; a heating operation of heating the wire in a state in which tension is applied; a cooling operation of cooling the wire; and a straightness measurement operation of winding the wire around a winding portion having a diameter greater than a diameter of the wire for a preset period of time and then measuring straightness of the wire, wherein, when measuring the straightness of the wire of 400 mm in the straightness measurement operation, the straightness of the wire is less than or equal to 30 mm.

The wire may include a plurality of wires, wherein the method further includes a stranding operation of twisting and stranding the plurality of wires to each other.

A heating temperature in the heating operation may be about 80° C. to about 220° C.

The heating temperature and a heating time in the heating operation of the wire may satisfy Equation A below, and the heating temperature in the heating operation may be higher than or equal to 80° C., wherein Equation A: T+15.67 ln(t)≥300, wherein T denotes absolute temperature K of the heating temperature, and t denotes the heating time s.

The heating time in the heating operation may be about 0.02 s to about 10 s, and tension applied to the wire in the heating operation may be about 1% to about 50% of a cutting strength.

Advantageous Effects of Disclosure

The present disclosure relates to a steel wire having excellent straightness quality and a manufacturing method thereof, wherein as the steel wire is heated at a preset temperature or higher for a short period of time, strain aging of the steel wire may be promoted to improve straightness quality after aging.

Also, as the steel wire is heated at the preset temperature or higher for the short period of time, a microstructure of the steel wire may not significantly change. Therefore, strain aging of the steel wire may be promoted without deteriorating physical properties of the steel wire to improve the straightness quality after aging.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating measuring straightness of a steel wire having excellent straightness quality, according to an embodiment;

FIG. 2 is a graph illustrating productivity according to heating time of a steel wire having excellent straightness quality, according to an embodiment;

FIG. 3 is a table illustrating straightness when manufacturing a steel wire by applying tension of 1% of a cutting strength and heating a wire while changing a heating time and a heating temperature of the wire, according to an embodiment;

FIG. 4 is a table illustrating straightness when manufacturing a steel wire by applying tension of 5% of a cutting strength and heating a wire while changing a heating time and a heating temperature of the wire, according to an embodiment;

FIG. 5 is a table illustrating straightness when manufacturing a steel wire by applying tension of 15% of a cutting strength and heating a wire while changing a heating time and a heating temperature of the wire, according to an embodiment;

FIG. 6 is a table illustrating straightness when manufacturing a steel wire by applying tension of 30% of a cutting strength and heating a wire while changing a heating time and a heating temperature of the wire, according to an embodiment;

FIG. 7 is a table illustrating straightness when manufacturing a steel wire by applying tension of 50% of a cutting strength and heating a wire while changing a heating time and a heating temperature of the wire, according to an embodiment;

FIG. 8 is a table illustrating straightness when manufacturing a steel wire by applying tension of 1% of a cutting strength and heating a wire while increasing a heating time of the wire, according to an embodiment;

FIG. 9 is a table illustrating Equation A values according to heating temperature and heating time and straightness values after 30 days, according to an embodiment;

FIG. 10 is a graph illustrating changes in a tensile strength of a wire according to heating temperature; and

FIG. 11 is a flowchart illustrating a method of manufacturing a steel wire having excellent straightness quality, according to an embodiment.

MODE OF DISCLOSURE

The present disclosure relates to a steel wire having excellent straightness quality and a manufacturing method thereof, wherein as the steel wire is heated at a preset temperature or higher for a short period of time, strain aging of the steel wire is promoted to improve straightness quality after aging. Example embodiments will now be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, a steel wire having excellent straightness quality according to an embodiment includes a wire 110 that, after undergoing a drawing operation, undergoes a heating operation of performing heating in a state in which tension is applied and undergoes a cooling operation. Although the wire 110 is wound around a wining portion for a preset period of time or more, straightness thereof is less than or equal to 30 mm.

Referring to FIG. 1, straightness according to an embodiment may be measured as follows. The wire 110 is wound around a winding portion having a diameter greater than a diameter of the wire 110 for a preset period of time. Thereafter, an end 111 of the wire 110 that is wound is fixed to a point 120, and the wire 110 is vertically lowered. Here, the wire 110 is lowered to 400 mm. In other words, a distance between the end 111 of the wire 110 and an other end 112 of the wire 110 is 400 mm.

Straightness of the wire 110 may be determined by an interval between a first axis 121 forming a vertical line from the point 120 and the other end 112 of the wire 110. In detail, as the interval between the first axis 121 and the other end 112 of the wire 110 is narrow, the steel wire has excellent straightness, and as the interval between the first axis 121 and the other end 112 of the wire 110 is wide, the steel wire has poor straightness.

As the steel wire according to the embodiment is heated at a preset temperature or higher for a short period of time to promote strain aging of the steel wire, when measuring the straightness after winding the wire 110 around the winding portion for a preset period of time, the straightness of the wire 110 may be maintained to be less than or equal to 30 mm. (Here, the preset period of time for which the wire 110 is wound around the winding portion may be about six months to about one year but is not limited thereto.)

The wire 110 according to the embodiment may be formed of a carbon steel material, and the wire 110 may be formed of a carbon steel material of about 0.5 wt % to about 1.1 wt %.

After undergoing a drawing operation, the wire 110 may be heated in a state in which tension is applied, and the undergoing of the drawing operation may indicate that the wire 110 may undergo a process including a drawing process. In detail, patenting processing may be performed for the wire 110 to secure high strength and processability. A pearlite microstructure that is an aggregation of carbon-based cementite and ferrite formed of Fe is acquired by performing patenting processing for the wire 110.

A plurality of wires 110 that undergo the drawing process may be provided and may undergo a stranding operation of twisting and stranding the plurality of wires 110 to each other. However, the stranding operation may be omitted as needed, and thus, when the wire 110 is used as a single steel wire, the stranding operation may be omitted.

The drawing process is a process that involves a large deformation in a material and deforms a pearlite structure of high carbon steel and promotes decomposition of cementite in a lamellar layer. When the cementite is decomposed by the deformation occurring in the drawing process, fractions of interstitial solid solution atoms C and N in ferrite matrix increase.

Here, strain aging occurs as an interstitial solid solution atom such as C or N fixes to a potential over time, and factors thereof may include not only a density of a solid solution atom, but also time, temperature, a density of a potential, and the like. Moreover, through the drawing process, a high-density potential exists inside a material accompanied by large plastic deformation, and an aging phenomenon is further promoted.

In other words, when the steel wire that is completely drawn is wound around a spool having a preset inner diameter, cementite is decomposed over time to produce strain aging, a change in straightness is accompanied, and thus, targeted straightness may not be acquired.

To prevent this, the wire 110 according to the embodiment undergoes a heating operation in which the same is heated in a state in which tension is applied and then undergoes a cooling operation, thereby artificially promoting and completing diffusion of solid solution atoms. As the diffusion of the solid solution atoms is artificially promoted and completed as described above, even after the wire 110 is wound around the winding portion having a preset inner diameter, an aging phenomenon does not occur in the wire 110.

As described above, the steel wire according to the embodiment is capable of improving the straightness thereof by promoting the strain aging of the wire 110, but the strain aging may be promoted not to affect other physical properties of the wire 110.

For this, a heating time in the heating operation of the wire 110 according to the embodiment may be about 0.02 s to about 10 s and may also be about 0.02 s to about 5 s.

When the wire 110 is heated for too long in the heating operation of the wire 110, the strain aging of the wire 110 may be promoted, but productivity of steel wire manufacturing may decrease.

Referring to FIG. 2, as a heating time becomes longer in the heating operation of the wire 110, productivity of the steel wire decreases, and the productivity rapidly decreases at the heating time longer than or equal to 10 s. In other words, when the heating time increases in the heating operation of the wire 110, as a productivity speed slows down, the productivity may decrease, and thus, manufacturing cost may increase.

Also, when the wire 110 is not heated for a sufficient time in the heating operation of the wire 110, strain aging is not promoted. In detail, at the heating time of 0.01 s shorter than 0.02 s in the heating operation of the wire 110, as the heating time is too short, carbon atoms decomposed from cementite at an interface between cementite and ferrite do not have an enough driving force to move into a ferrite area, and thus, an acceleration where carbon is fixed to a potential does not occur. Therefore, the heating time in the heating operation of the wire 110 may be about 0.02 s to about 10 s and may also be about 0.02 s to about 5 s.

At the same time, a heating temperature and the heating time in the heating operation of the wire 110 according to the embodiment may satisfy Equation A below, and the heating temperature in the heating operation of the wire 110 may be higher than or equal to 80° C. Equation A: T+15.67 ln(t)≥300, wherein T denotes absolute temperature K of the heating temperature, and t denotes the heating time s.

Referring to FIGS. 3 through 7, when the heating temperature and the heating time in the heating operation of the wire 110 do not satisfy Equation A, the strain aging of the wire 110 is not sufficiently promoted, and thus the straightness of the wire 110 is not improved.

(FIG. 3 illustrates that the wire 110 is heated while applying tension of 1% of a cutting strength thereto, FIG. 4 illustrates that the wire 110 is heated while applying tension of 5% of the cutting strength thereto, FIG. 5 illustrates that the wire 110 is heated while applying tension of 15% of the cutting strength thereto, FIG. 6 illustrates that the wire 110 is heated while applying tension of 30% of the cutting strength thereto, and FIG. 7 illustrates that the wire 110 is heated while applying tension of 50% of the cutting strength thereto. Numerical values in FIGS. 3 through 7 are measured from the straightness of the wire 110 through a straightness measurement method as described above.)

Here, the heating temperature of the wire 110 may be higher than or equal to 80° C. When the heating temperature of the wire 110 is lower than 80° C., although the heating temperature and the heating time in the heating operation of the wire 110 satisfy Equation A, the strain aging of the wire 110 is not promoted.

In detail, embodiments of 60° C.—1 s and 40° C.—1 s in FIG. 3, 60° C.—1 s and 40° C.—1 s in FIG. 4, 60° C.—1 s and 40° C.—1 s in FIG. 5, 60° C.—1 s and 40° C.—1 s in FIG. 6, and 60° C.—1 s and 40° C.—1 s in FIG. 7 satisfy Equation A, but as the heating temperature is lower than 80° C., the strain aging is not promoted, and thus, the straightness becomes poor.

FIG. 8 illustrates that the heating temperature of the wire 110 is lower than 80° C., and the heating time becomes longer (longer than or equal to 10 seconds). Referring to FIG. 8, although the heating time becomes longer at the heating temperature lower than 80° C., the strain aging of the wire 110 is not promoted. As described above, when the heating temperature of the wire 110 is lower than 80° C., although the heating time of the wire 110 becomes longer, the strain aging is not promoted.

The strain aging occurs as an interstitial solid solution atom such as C or N fixes to a potential over time, and factors thereof may include not only a density of the solid solution atom, but also time, temperature, a density of a potential, and the like. In other words, a preset temperature is needed to fix an interstitial solid solution atom such as C or N to a potential over time, and when the heating temperature of the wire 110 is lower than 80° C., the interstitial solid solution atom such as C or N is not fixed to the potential over time, and thus the strain aging is not promoted.

Therefore, although the heating temperature and the heating time in the heating operation of the wire 110 satisfy Equation A, when the heating temperature in the heating operation is lower than 80° C., the strain aging is not promoted.

Also, although the heating temperature in the heating operation of the wire 110 is higher than 80° C., when the heating temperature and the heating time in the heating operation of the wire 110 do not satisfy Equation A, the strain aging is not promoted. In detail, with reference to 80° C.—0.01 s, 0.02 s, and 0.03 s in FIG. 9, since the heating temperature in the heating operation is higher than or equal to 80° C. but does not satisfy Equation A, the strain aging is not promoted, and thus, the straightness is not improved.

Also, although the heating temperature in the heating operation of the wire 110 is higher than or equal to 80° C., when the heating time in the heating operation of the wire 110 is shorter than 0.02 s, the strain aging is not promoted. In detail, with reference to 100° C.—0.01 s, 150° C.—0.01 s, and 200° C.—0.01 s in FIG. 9, since the heating temperature in the heating operation is higher than or equal to 80° C. and satisfies Equation A, but the heating time is insufficient, the strain aging is not promoted.

This is because the heating time in the heating operation of the wire 110 is considerably short. Although the heating temperature in the heating operation of the wire 110 is higher than or equal to 80° C., when the heating time in the heating operation of the wire 110 is considerably short, the interstitial solid solution atom such as C or N is not fixed to the potential over time, and thus, the strain aging is not promoted.

Therefore, the heating temperature and the heating time in the heating operation of the wire 110 may satisfy Equation A below, and the heating temperature in the heating operation of the wire 110 may be higher than or equal to 80° C. In other words, although the heating temperature is higher than or equal to 80° C., when the heating time is too short, the strain aging is not promoted, and thus, the heating time in the heating operation of the wire 110 may be longer than or equal to 0.02 s.

According to an embodiment, tension applied to the wire 110 in the heating operation of the wire 110 may be about 1% to about 50% of a cutting strength. The tension applied to the wire 110 in the heating operation of the wire 110 affects the heating temperature and the heating time.

As described above, the heating operation promotes the strain aging through the diffusion of interstitial solid solution atoms, and when the tension applied to the wire 110 increases, the straightness of the wire 110 increases, and a more excellent straightness improvement effect is exhibited under the same heating conditions. Therefore, the tension applied to the wire 110 in the heating operation of the wire 110 may be greater than 1% of the cutting strength.

However, when the tension applied to the wire 110 in the heating operation of the wire 110 is too great, physical properties of the wires 110 may be deteriorated by the tension. Therefore, the tension applied to the wire 110 in the heating operation of the wire 110 may be less than 50% of the cutting strength. (Here, a cutting strength is one of physical properties of a wire and refers to a strength at a point in time at which the wire is cut when tension is applied from both ends of the wire to an axial direction.)

However, the tension applied to the wire 110 is not limited to about 1% to about 50% of the cutting strength, and appropriate tension may be applied as needed.

The heating temperature in the heating operation of the wire 110 according to an embodiment may be about 80° C. to about 220° C. The point that the heating temperature may be higher than or equal to 80° C. is the same as described above and thus is omitted herein. Referring to FIG. 10, when the heating temperature is lower than or equal to 220° C. in the heating operation of the wire 110, a tensile strength may be increased without significantly changing a microstructure.

However, when the heating temperature becomes excessively higher than 220° C., a physical property aspect of the wire 110 becomes inappropriate enough to observe changes in the microstructure, and the tensile strength gradually decreases. In other words, when the heating temperature is higher than 220° C., the strain aging may be promoted, but the tensile strength of the wire 110 may decrease. Therefore, the heating temperature in the heating operation of the wire 110 may be about 80° C. to about 220° C.

The steel wire having the excellent straightness quality according to the embodiment described above may be manufactured by the following method. All of the properties of the steel wire having the excellent straightness quality described above may be applied to a method of manufacturing a steel wire having excellent straightness quality according to an embodiment, which will be described below.

Referring to FIG. 11, the method according to the embodiment includes a wire preparation operation S110, a heating operation S130, a cooling operation S140, and a straightness measurement operation S150.

The wire preparation operation S110 is an operation of preparing a drawn wire. When the wire preparation operation S110 includes an operation of drawing the wire 110, various types of processes may be included therein.

The method of manufacturing the steel wire having the excellent straightness quality according to the embodiment may further include a stranding operation S120. The stranding operation S120 is an operation of providing a plurality of wires 110, and twisting and stranding the plurality of wires 110 to each other. The stranding operation S120 may be included when manufacturing a steel wire including stranded wires but may be omitted when manufacturing a single steel wire.

The heating operation S130 is an operation of heating the wire 110 that is drawn, in a state in which tension is applied. In the heating operation S130, a heating temperature may be about 80° C. to about 220° C.

Also, the heating temperature and a heating time in the heating operation S130 may satisfy Equation A: T+15.67 ln(t)≥300 (wherein T denotes absolute temperature K of the heating temperature, and t denotes the heating time s), and the heating temperature in the heating operation S130 may be higher than or equal to 80° C.

Also, the heating time in the heating operation S130 may be about 0.02 s to about 10 s, and tension applied to the wire 110 in the heating operation 130 may be about 1% to about 50% of a cutting strength. However, the tension applied to the wire 110 is not limited to about 1% to about 50% of the cutting strength, and thus appropriate tension may be applied as needed.

The delimited significance of numerical values of the heating temperature, the heating time, and the tension in the heating operation S130 is the same as described above in the steel wire having the excellent straightness quality according to the embodiment, and thus detailed description thereof is omitted herein.

The cooling operation S140 is an operation of cooling the wire 110 that undergoes the heating operation S130. Since the wire 110 that undergoes the heating operation S130 is exposed to an environment appropriate to diffuse C and N in the wire 110, when cooling is insufficiently performed, and winding is performed, strain aging may not be completely suppressed. Therefore, the wire 110 that undergoes the heating operation S130 may be cooled in the cooling operation S140.

A cooling temperature in the cooling operation S140 may be lower than or equal to 50° C., and as the cooling temperature in the cooling operation S140 is low, an effect may be increased, and thus, cooling may be performed at a cooling temperature lower than or equal to 50° C. In detail, the cooling operation S140 may be performed at room temperature. However, the cooling temperature in the cooling operation S140 is not limited thereto and may be changed as needed. The cooling operation S140 may be performed in various methods, and methods such as air cooling, reducing and inert gas cooling, water cooling, and the like may be used.

The straightness measurement operation S150 is an operation of winding the wire 110 around a winding portion having a diameter greater than a diameter of the wire 110 for a preset period of time and then measuring straightness of the wire 110.

Referring to FIG. 1, the straightness may be measured in the straightness measurement operation S150 as follows. The wire 110 is wound around the winding portion having the diameter greater than the diameter of the wire 110 for the preset period of time. Thereafter, the end 111 of the wire 110 that is wound is fixed to the point 120, and the wire 110 is vertically lowered. Here, the wire 110 is lowered to 400 mm. In other words, a distance between the end 111 of the wire 110 and the other end 112 of the wire 110 is 400 mm.

The straightness of the wire 110 measured in the straightness measurement operation S150 may be an interval between the first axis 121 forming a vertical line from the point 120 and the other end 112 of the wire 110. In detail, as the interval between the first axis 121 and the other end 112 of the wire 110 is narrow, the steel wire has excellent straightness, and as the interval between the first axis 121 and the other end 112 of the wire 110 is wide, the steel wire has poor straightness.

In the method of manufacturing the steel wire having the excellent straightness quality according to the embodiment, when winding the wire 110 around the winding portion for the preset period of time as in the method described above and then measuring the straightness of the wire 110 of 400 mm in the straightness measurement operation S150, a steel wire including the wire 110 having straightness less than or equal to 30 mm may be manufactured.

The steel wire having the excellent straightness quality and the method of manufacturing the same according to the embodiments as described above have the following effects.

In the steel wire having the excellent straightness quality and the method of manufacturing the same according to the embodiments, as the steel wire is heated at a preset temperature for a short period of time, strain aging of the steel wire may be promoted to improve the straightness quality after aging.

Also, in the steel wire having the excellent straightness quality and the method of manufacturing the same according to the embodiments, as the steel wire is heated at the preset temperature for the shorter period of time, a microstructure of the steel wire may not be significantly changed, and thus, the strain aging may be promoted without deteriorating physical properties of the steel wire to improve the straightness quality after aging.

In detail, in the steel wire having the excellent straightness quality and the method of manufacturing the same according to the embodiments, as a wire is heated for a short period of time (about 0.02 s to about 10 s or about 0.02 s to about 5 s), straightness of the wire may be improved without changing physical properties of the wire.

Here, to promote the strain aging of the wire while heating the wire for the short period of time, a heating temperature and a heating time in a heating operation of the wire may satisfy Equation A: T+15.67 ln(t)≥300 (wherein T denotes absolute temperature K of the heating temperature, and t denotes the heating time s), and the heating temperature in the heating operation may be higher than or equal to 80° C.

Referring to FIGS. 3 through 9, when the conditions as described above are not satisfied, the strain aging is insufficiently promoted. However, in the steel wire having the excellent straightness quality according to the embodiment, the wire may be heated while satisfying the above conditions, and thus, the straightness of the wire may be improved without changing the physical properties of the wire.

In a steel wire having excellent straightness quality and a method of manufacturing the same according to embodiments, Equation A: T+15.67 ln(t)≥300 (wherein T denotes absolute temperature K of the heating temperature, and t denotes the heating time s) may be modified as follows. Equation A above may be modified into 420≥T+15.67 ln(t)≥300, and Equation A may have an upper limit of 420.

As values of the heating temperature and the heating time increase, and a value of Equation A increases, the strain aging may be promoted. However, when the upper limit of Equation A exceeds 420, economic and workability aspects may be inefficient. Also, as the values of the heating temperature and the heating time are increased to exceed the upper limit of 420 in Equation A, a risk of affecting the physical properties of the wire may increase, and thus, Equation A above may be formed of 420 T+15.67 ln(t)≥300.

While the present disclosure has been particularly shown and described with reference to example embodiments thereof, the present disclosure is not limited to the embodiments, and various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure. Therefore, the scope of the present disclosure should be defined by the spirit of the appended claims. 

1. A steel wire needing straightness having excellent straightness quality, the steel wire comprising: a wire, after undergoing a drawing operation, undergoing a heating operation of performing heating in a state in which tension is applied, and undergoing a cooling operation, wherein, when winding the wire around a winding portion having a diameter greater than a diameter of the wire for a preset period of time and then measuring straightness of the wire of 400 mm, the straightness of the wire is less than or equal to 30 mm.
 2. The steel wire of claim 1, wherein a heating temperature in the heating operation is about 80° C. to 220° C.
 3. The steel wire of claim 2, wherein the heating temperature and a heating time in the heating operation of the wire satisfy Equation A below, and the heating temperature in the heating operation is higher than or equal to 80° C., wherein Equation A: T+15.67 ln(t)≥300, wherein T denotes absolute temperature K of the heating temperature, and t denotes the heating time s.
 4. The steel wire of claim 3, wherein the heating time in the heating operation is about 0.02 s to about 10 s.
 5. The steel wire of claim 1, wherein tension applied to the wire in the heating operation is about 1% to about 50% of a cutting strength.
 6. A method of manufacturing a steel wire needing straightness having excellent straightness quality, the method comprising: a wire preparation operation of preparing a wire that is drawn; a heating operation of heating the wire in a state in which tension is applied; a cooling operation of cooling the wire; and a straightness measurement operation of winding the wire around a winding portion having a diameter greater than a diameter of the wire for a preset period of time and then measuring straightness of the wire, wherein, when measuring the straightness of the wire of 400 mm in the straightness measurement operation, the straightness of the wire is less than or equal to 30 mm.
 7. The method of claim 6, wherein the wire comprises a plurality of wires, wherein the method further comprises a stranding operation of twisting and stranding the plurality of wires to each other.
 8. The method of claim 6, wherein a heating temperature in the heating operation is about 80° C. to about 220° C.
 9. The method of claim 8, wherein the heating temperature and a heating time in the heating operation of the wire satisfy Equation A below, and the heating temperature in the heating operation is higher than or equal to 80° C., wherein Equation A: T+15.67 ln(t)≥300, wherein T denotes absolute temperature K of the heating temperature, and t denotes the heating time s.
 10. The method of claim 9, wherein the heating time in the heating operation is about 0.02 s to about 10 s.
 11. The method of claim 6, wherein tension applied to the wire in the heating operation is about 1% to about 50% of a cutting strength. 